1. Field of the Invention
This invention relates to a magnetic fluid used at seal rings of shafts, etc., a method for producing such a magnetic fluid, and a magnetic seal means using the same.
2. Prior Art
Hitherto, magnetic fluids have generally been produced by a method in which the surfaces of fine particles of a ferromagnetic material such as fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4 or Co-added .gamma.-Fe.sub.2 O.sub.3 are coated with a surfactant such as oleic acid, and said coated particles are dispersed in an oil such as kerosene.
The above-described conventional method, however, although simple and easy to carry out, had the problem that since the surfactant such as oleic acid only adheres to the surfaces of the fine particles of a magnetic material, said surfactant would dissociate from the particle surfaces after long-term use, causing agglomeration of said particles. Thus, the magnetic fluid produced by said conventional method was low in reliability and unsatisfactory in performance for use as a sealant in high-vacuum systems.